Electrophotographic technology, which is used in, for example, copiers, printers, facsimile machines, and so forth, is continuing to expand and develop. With regard to recent trends, there is increasing demand for the ability to carry out high-speed printing and in another vein there is increasing demand for smaller sizes and better energy savings.
Within the toner sphere, for example, the fixing temperature has been lowered by lowering the glass transition temperature of the resin that is used in the toner particles. In addition, such toner generally is also favorable in terms of image glossiness. However, a toner that has a low glass transition temperature, while exhibiting an excellent low-temperature fixability, is prone to suffer from a reduced long-term storability, environmental stability, or durability, and quite a few means for satisfying the required properties have been proposed to date. For example, a large number of toners having a core-shell structure have been proposed in order to provide a toner that is equipped with both low-temperature fixability and durability and long-term storability. In one example here, both a low-temperature fixability and durability are achieved by lowering the glass transition temperature of the resin used in the core and coating the surface with a resin that has a high glass transition temperature.
However, it is becoming quite problematic to achieve a toner equipped with both low-temperature fixability and durability and long-term storability, for which the required performance levels are increasing year by year, just by improving the core-shell structure.
In addition, it has in the past been believed in the toner field that the surfactant must be removed to the maximum possible degree because surfactant impairs various properties when it is present in toner. Patent document 1 teaches that less nonionic surfactant is better. On the other hand, there are some documents that focus on nonionic surfactant at the toner surface. For example, Patent document 2 discloses that a toner that has an excellent low-temperature fixability and an excellent environmental stability is obtained by specifying the type of the external additive and the nonionic surfactant at the toner surface, and coverage ratio of them. In addition, Patent document 3 discloses that a toner that exhibits excellent charging characteristics and environmental stability is obtained by specifying the residual surfactant and the divalent metal ion originating from the aggregating agent, which are in the toner.